In the oil and gas industry, exploration and extraction processes often require deep wells to be drilled with a long drill string rotating in a long hole. The interaction between the drill string and the well wall introduces a heavy abrasive load, which further develops a very high torque on the drill string and a very large friction force at the contact points between the drill string and the wall. The increase in the torque leads to greater energy consumption, while the friction may cause wear and damage to the drill string as well as the steel casing used to line sections of the well. Both of the above mentioned issues lead to economic loss create a competitive disadvantage for the drilling service providers. In addition, as drill strings get longer and heavier with addition of more drilling pipes, flexibility increase with more risk of lateral deflection from its expected axis. The deflection may induce wobbling of the drill bit, and further reduce the drilling rate and increase severe deviation of the hole.
The issue is well known and great effort has been made to overcome drill string friction and deflection problems. One solution involves a rotating collar for the well operations to prevent friction against a well casing using ball bearing to allow the collar rotating freely relative to the drill string. Another solution involves a drill string bushing tool which is clamped onto the drill string. The bushing tool includes a rigid tubular reinforcing metallic inner sleeve having rubber-like material molded on both the inner and the outer sides of the sleeve. Multiple drill string bushing tools can be disposed on a rotary drill string and allow relative rotation with respect to it to avoid the drill string deflection.
Another system involves using a friction reducing component mounted as a sub in the drill string having a double-sleeve mounted on a mandrel via bearings. The inner sleeve is secured on the mandrel, while the outer sleeve is mounted onto the inner sleeve by way of bushings that allows it rotate freely. As the sleeve is rotatable on the mandrel and non-rotating (stationary) relative to the well wall, this type of sub is classified as “non-rotating” subs.
However, the above mentioned methods have limited industrial deployment due to issues on cost, complexity and operation. A friction-reducing component with features of simple construction for easy manufacturing, operating and maintaining as well as reasonable low cost is still highly demanded.